The present invention deals with sensors. More specifically, the present invention deals with a junction in a sensor which provides continuity between one solution and another solution.
Electrochemical sensors are commonly used to sense characteristics of a solution of interest. Conventional electrochemical sensors typically have an outer housing which defines a cavity filled with an internal or reference solution. A reference electrode is disposed within the reference solution. In addition, conventional electrochemical sensors typically have an inner body or housing, disposed within the inner cavity of the outer housing, which supports an ion selective electrode. The ion selective electrode extends out from within the cavity defined by the outer housing to contact a solution of interest to be analyzed.
A reference junction is commonly used in an attempt to substantially seal the cavity defined by the outer housing, other than where the ion selective electrode exits the cavity, so that the reference solution does not mix with, and become diluted by, the solution of interest. The reference junction maintains ionic communication between the reference solution and the solution of interest to enable accurate electrochemical measurements.
A disadvantage of such electrochemical sensors is limited useful lifetime as a result of degradation of the reference electrode due to ion exchange between the retained solution and the solution of interest. Prior attempts to extend the useful life involve modifying the electrochemical reference junction between the internal solution and the solution of interest. However, these attempts have typically required a discrete, specific junction component which is in addition to the outer housing and the other components required by the electrochemical sensor.
Such prior junctions provide an ionic leak between the internal solution and the solution of interest. The prior junctions have included an orifice, bundles of minuscule tubes which provide means of ionic migration, matrices of grains or open cells, and ion permeable membranes or solids, all of which provide an ionic leak between the internal solution and the solution of interest. These potential solutions have a disadvantage in that they require a separate, discrete component to be used in forming the ionic reference junction in the electrochemical sensor.
A number of these solutions have other deficiencies as well, such as difficulty of manufacture and fragility in industrial applications.